In renewal demands of various types of air conditioners, existing refrigerant piping is often re-used as it is. In such a case, if a refrigerant for the existing refrigerant circuit and a refrigerant for a new refrigerant circuit are the same CFC (chlorofluorocarbon) or HCFC (hydrochlorofluorocarbon) refrigerant, the existing refrigerant piping can be used without causing any significant problems.
However, from the recent years' environmental point of view or the like, it has been proposed to use HFC (hydrofluorocarbon) refrigerants instead of conventional CFC or HCFC refrigerants.
In this case, for reuse of the existing refrigerant piping, it is necessary to clean the interior of the refrigerant piping. That is, it is often the case that lubricating oil have been deposited on or contaminants or the like have stuck to the interior surfaces of the existing refrigerant piping. In particular, whereas mineral oil has been used lubricating oil for conventional CFC refrigerants and the like, synthetic oil is used as lubricating oil for HFC refrigerants. This causes a problem that mineral oil, if remaining in the existing refrigerant piping, would cause contaminations to occur to a newly provided refrigerant circuit, with the result that the throttle mechanism may be blocked or that the compressor may be damaged.